FIG. 2.28

Could the building blocks of organic molecules have been generated on the early Earth?

BACKGROUND In the 1950s, Earth’s early atmosphere was widely believed to have been rich in water vapor, methane, ammonia, and hydrogen gas, with no free oxygen.

EXPERIMENT Stanley Miller built an apparatus, shown below, designed to simulate Earth’s early atmosphere. Then he passed a spark through the mixture to simulate lightning.

RESULTS As the experiment proceeded, reddish material accumulated on the walls of the flask. Analysis showed that the brown matter included a number of amino acids.

CONCLUSION Amino acids can be generated in conditions that mimic those of the early Earth.

FOLLOW-UP WORK Recent analysis of the original extracts, saved by Miller, shows that the experiment actually produced about 20 different amino acids, not all of them found in organisms.

SOURCES Miller, S. L. 1953. “Production of Amino Acids Under Possible Primitive Earth Conditions.” Science 117:528–529; Johnson, A. P., et al. 2008. “The Miller Volcanic Spark Discharge Experiment.” Science 322:404.